/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package cn.newtest.common.filter;

import java.io.IOException;
import java.util.Enumeration;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Implementation of <code>javax.servlet.Filter</code> used to compress the
 * ServletResponse if it is bigger than a threshold.
 * 
 * @author Amy Roh
 * @author Dmitri Valdin
 * @version $Revision: 1.1 $, $Date: 2009/03/18 11:23:00 $
 */

public class CompressionFilter implements Filter {

	/**
	 * The filter configuration object we are associated with. If this value is
	 * null, this filter instance is not currently configured.
	 */
	private FilterConfig config = null;

	/**
	 * Minimal reasonable threshold
	 */
	private int minThreshold = 128;

	/**
	 * The threshold number to compress
	 */
	protected int compressionThreshold;

	/**
	 * Debug level for this filter
	 */
	private int debug = 0;

	/**
	 * Place this filter into service.
	 * 
	 * @param filterConfig
	 *            The filter configuration object
	 */

	public void init(FilterConfig filterConfig) {

		config = filterConfig;
		if (filterConfig != null) {
			String value = filterConfig.getInitParameter("debug");
			if (value != null) {
				debug = Integer.parseInt(value);
			} else {
				debug = 0;
			}
			String str = filterConfig.getInitParameter("compressionThreshold");
			if (str != null) {
				compressionThreshold = Integer.parseInt(str);
				if (compressionThreshold != 0
						&& compressionThreshold < minThreshold) {
					if (debug > 0) {
						System.out
								.println("compressionThreshold should be either 0 - no compression or >= "
										+ minThreshold);
						System.out.println("compressionThreshold set to "
								+ minThreshold);
					}
					compressionThreshold = minThreshold;
				}
			} else {
				compressionThreshold = 0;
			}

		} else {
			compressionThreshold = 0;
		}

	}

	/**
	 * Take this filter out of service.
	 */
	public void destroy() {

		this.config = null;

	}

	/**
	 * The <code>doFilter</code> method of the Filter is called by the
	 * container each time a request/response pair is passed through the chain
	 * due to a client request for a resource at the end of the chain. The
	 * FilterChain passed into this method allows the Filter to pass on the
	 * request and response to the next entity in the chain.
	 * <p>
	 * This method first examines the request to check whether the client
	 * support compression. <br>
	 * It simply just pass the request and response if there is no support for
	 * compression.<br>
	 * If the compression support is available, it creates a
	 * CompressionServletResponseWrapper object which compresses the content and
	 * modifies the header if the content length is big enough. It then invokes
	 * the next entity in the chain using the FilterChain object (<code>chain.doFilter()</code>),
	 * <br>
	 */

	public void doFilter(ServletRequest request, ServletResponse response,
			FilterChain chain) throws IOException, ServletException {

		if (debug > 0) {
			System.out.println("@doFilter");
		}

		if (compressionThreshold == 0) {
			if (debug > 0) {
				System.out
						.println("doFilter gets called, but compressionTreshold is set to 0 - no compression");
			}
			chain.doFilter(request, response);
			return;
		}

		boolean supportCompression = false;
		if (request instanceof HttpServletRequest) {
			if (debug > 1) {
				System.out.println("requestURI = "
						+ ((HttpServletRequest) request).getRequestURI());
			}

			// Are we allowed to compress ?
			String s = (String) ((HttpServletRequest) request)
					.getParameter("gzip");
			if ("false".equals(s)) {
				if (debug > 0) {
					System.out
							.println("got parameter gzip=false --> don't compress, just chain filter");
				}
				chain.doFilter(request, response);
				return;
			}

			Enumeration e = ((HttpServletRequest) request)
					.getHeaders("Accept-Encoding");
			while (e.hasMoreElements()) {
				String name = (String) e.nextElement();
				if (name.indexOf("gzip") != -1) {
					if (debug > 0) {
						System.out.println("supports compression");
					}
					supportCompression = true;
				} else {
					if (debug > 0) {
						System.out.println("no support for compresion");
					}
				}
			}
		}

		if (!supportCompression) {
			if (debug > 0) {
				System.out.println("doFilter gets called wo compression");
			}
			chain.doFilter(request, response);
			return;
		} else {
			if (response instanceof HttpServletResponse) {
				CompressionServletResponseWrapper wrappedResponse = new CompressionServletResponseWrapper(
						(HttpServletResponse) response);
				wrappedResponse.setDebugLevel(debug);
				wrappedResponse.setCompressionThreshold(compressionThreshold);
				if (debug > 0) {
					System.out.println("doFilter gets called with compression");
				}
				try {
					chain.doFilter(request, wrappedResponse);
				} finally {
					wrappedResponse.finishResponse();
				}
				return;
			}
		}
	}

	/**
	 * Set filter config This function is equivalent to init. Required by
	 * Weblogic 6.1
	 * 
	 * @param filterConfig
	 *            The filter configuration object
	 */
	public void setFilterConfig(FilterConfig filterConfig) {
		init(filterConfig);
	}

	/**
	 * Return filter config Required by Weblogic 6.1
	 */
	public FilterConfig getFilterConfig() {
		return config;
	}

}
